Recently, for display and so on, attention has been paid to organic EL elements and they have been researched. In general, organic EL elements basically have a transparent electrode (anode), a luminous layer made of an organic material, and an opposite electrode (cathode). Many of the organic EL elements further have an electron injection layer, a hole injection layer and so on, in order to improve luminescent property, and have a structure wherein these are deposited into a lamination on a substrate. This is a principle that luminescence is caused by recombination in the luminous layer of an electron injected from the cathode to the luminous layer with a hole injected from the anode to the luminous layer.
For elements having a structure wherein thin film layers are deposited into a lamination, such as organic EL elements as described above, the respective layers are deposited by vacuum evaporation in many cases.
However, if thin film layers are deposited into a lamination on a substrate having a large screen by this vacuum evaporation, a problem that homogeneous films cannot be formed arises. Therefore, many substrate pieces cannot be arranged in a substrate of a large area so that mass production is not allowed. If a large-sized device is produced, luminescence variation is generated in the luminous plane thereof so that the device becomes a defective product.
Against such problems, JP-A-10-335062 suggests a method in which the relationship between the deposition position, on a substrate, of a material, and the vapor density thereof is represented by a function of cosnθ, the n value thereof is set to 3 to 6, and an evaporation source thereof is set to a position apart from the center of the substrate. By this method, however, it is difficult to form a homogenous thin film on a substrate having a large screen. Thus, the variation of luminescence performance cannot be overcome just yet. Accordingly, the following points are unsolved problems from the viewpoint that in an organic EL element or the like element which has a structure wherein thin film layers are deposited into a lamination on a substrate having a large screen, the homogeneity of luminescence performance at respective positions in the element is kept.
(1) In the case that thin films are deposited into a lamination, change in the film thickness of each of the films is large at respective positions on a deposition substrate. Thus, in the case of an organic EL element, the variation of luminescence performance is generated inside the plane of the element.
(2) In the case that, for an organic EL element or the like element, a host material and a dopant material of its luminous layer are co-evaporated as evaporation sources, the density of the dopant is not constant in the plane of the element so that the variation of luminescence performance is generated.
The present invention has been made from the above-mentioned viewpoints. An object of the present invention is to provide a method for depositing a homogeneous thin film layer for an element, even on a deposition substrate having a large screen, by vacuum evaporation, the method being capable of attaining the following. In the case of depositing many layers into a lamination, change in the film thickness of each of the films can be made small at respective positions on a deposition substrate. In the case of co-evaporating plural evaporation sources, change in the density of each of the materials can be made small at respective positions on a deposition substrate.
Another object of the present invention is to provide an organic EL element which is produced by such a method for depositing a thin film layer for an element, and which is small in the variation of luminescence performance at respective positions in the element.